percpu_ref: release percpu memory early without PERCPU_REF_ALLOW_REINIT

Release percpu memory after finishing the switch to the atomic mode
if only PERCPU_REF_ALLOW_REINIT isn't set.

Signed-off-by: Roman Gushchin <guro@fb.com>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Dennis Zhou <dennis@kernel.org>

2 files changed, 12 insertions, 2 deletions

diff --git a/include/linux/percpu-refcount.h b/include/linux/percpu-refcount.h
index 0f0240af8520..7aef0abc194a 100644
--- a/include/linux/percpu-refcount.h
+++ b/include/linux/percpu-refcount.h
@@ -102,6 +102,7 @@ struct percpu_ref {
         percpu_ref_func_t       *release;
         percpu_ref_func_t       *confirm_switch;
         bool                    force_atomic:1;
+        bool                    allow_reinit:1;
         struct rcu_head         rcu;
 };
 
diff --git a/lib/percpu-refcount.c b/lib/percpu-refcount.c
index 9877682e49c7..501b517bd3db 100644
--- a/lib/percpu-refcount.c
+++ b/lib/percpu-refcount.c
@@ -69,11 +69,14 @@ int percpu_ref_init(struct percpu_ref *ref, percpu_ref_func_t *release,
                 return -ENOMEM;
 
         ref->force_atomic = flags & PERCPU_REF_INIT_ATOMIC;
+        ref->allow_reinit = flags & PERCPU_REF_ALLOW_REINIT;
 
-        if (flags & (PERCPU_REF_INIT_ATOMIC | PERCPU_REF_INIT_DEAD))
+        if (flags & (PERCPU_REF_INIT_ATOMIC | PERCPU_REF_INIT_DEAD)) {
                 ref->percpu_count_ptr |= __PERCPU_REF_ATOMIC;
-        else
+                ref->allow_reinit = true;
+        } else {
                 start_count += PERCPU_COUNT_BIAS;
+        }
 
         if (flags & PERCPU_REF_INIT_DEAD)
                 ref->percpu_count_ptr |= __PERCPU_REF_DEAD;
@@ -119,6 +122,9 @@ static void percpu_ref_call_confirm_rcu(struct rcu_head *rcu)
         ref->confirm_switch = NULL;
         wake_up_all(&percpu_ref_switch_waitq);
 
+        if (!ref->allow_reinit)
+                percpu_ref_exit(ref);
+
         /* drop ref from percpu_ref_switch_to_atomic() */
         percpu_ref_put(ref);
 }
@@ -194,6 +200,9 @@ static void __percpu_ref_switch_to_percpu(struct percpu_ref *ref)
         if (!(ref->percpu_count_ptr & __PERCPU_REF_ATOMIC))
                 return;
 
+        if (WARN_ON_ONCE(!ref->allow_reinit))
+                return;
+
         atomic_long_add(PERCPU_COUNT_BIAS, &ref->count);
 
         /*